1. Field of the Invention
The present invention relates generally to a rocker joint silent chain suitable for use in an automobile as a power transmission chain.
2. Description of the Related Art
A rocker joint silent chain used in an automobile is wound around more than two sprockets for transmitting power between the sprockets.
The rocker joint silent chain includes, as shown here in FIGS. 8 and 9, a multiplicity of sets of link plates A articulately connected together in an interleaved fashion by rocker joints C, with guide plates B located outside the set of link plates in the lateral direction for being guided on and along opposite end faces of the sprocket. Each set of link plates A is composed of a plurality of link plates A arranged in a row in the widthwise direction of the chain. Each link plate A has a pair of bifurcated engagement teeth A1, A1 spaced in a direction of travel of the chain for mesh with teeth of each sprocket (not shown), and a pair of pin-accommodation holes A2 spaced in the direction of travel of the chain. The guide plates B each have a pair of pin-accommodation holes B1 spaced in the direction of travel of the chain.
Each of the rocker joints C is composed of a cooperating pair of rocker joint pins C1 and C2 of different lengths. The longer rocker joint pin C1 and the shorter rocker joint pin C2 (hereinafter referred to, for brevity, as xe2x80x9clonger pinxe2x80x9d and xe2x80x9cshorter pinxe2x80x9d, respectively) are inserted in pair through each of the pin-accommodation holes A2 of the link plates A. The longer pin C2 is firmly fitted in each pin-accommodation hole B1 of the guide plates B and fixedly secured at its opposite ends to the guide plates B. The longer pin C1 and the shorter pin C2, which are used in combination, have respective convexly arcuate front surfaces held in contact with each other for rolling motion of the longer and shorter pins C1, C2 to permit the interleaved link plates A to pivot.
As best shown in FIG. 10, in the conventional rocker joint silent chain, each end of the shorter pin C2 is spaced a distance from the inside surfaces of a corresponding one of the guide plates B. Due to the presence of the clearance or gap G, the conventional rocker joint silent chain has a drawback, as described below.
In general, in a chain power transmission device composed of a power transmitting chain and two or more sprockets, the chain is likely to become loose or slack at its return side generally called xe2x80x9cslack sidexe2x80x9d because the chain tension at the slack side is extremely smaller than the chain tension at a stretched side generally called xe2x80x9ctension sidexe2x80x9d of the chain. This may cause flattering or resonant vibration of the chain especially when the sprockets are rotating at speeds below a operational speed range. In such instance, the chain travels in an advancing direction at irregular speeds while vibrating in vertical and horizontal directions.
In the case where the power transmitting chain consists of the afore-mentioned conventional rocker joint silent chain, wherein a clearance G is provided between each end of the shorter pin C2 and the inside surface of the corresponding guide plate B, as shown in FIG. 10, since the shorter pin C2 inserted through the pin-accommodating holes A2 (FIG. 8) of the link plates A is allowed to move freely within the range of the clearance G, the shorter pin C2 generates high-frequency contact noise or impact sound due to repeated contact with the inside surface of the pin-accommodation hole A2 and the convexly arcuate front surface of the longer pin C1.
The high-frequency contact noise or the impact sound is added to a meshing sound produced when the teeth of the chain come in mesh with the sprocket teeth with the result that the overall transmission noise level of the chain power transmission device increases greatly. In addition, the inside surface of the pin-accommodation hole A2 and the front surface of the longer pin C1 suffer from abrasive wear caused due to free movement of the shorter pin C2. This may hinder smooth mutual articulate movement of the link plates and shorten the service life of the chain.
To deal with this problem, an attempt may be made, in which a stopper member is provided to prevent the shorter pin C2 from moving freely. The stopper member, however, not only increases the number of parts used in the chain and the overall weight of the chain, but also makes the chain complicated in construction. This may cause additional difficulties in the manufacture and handling of the chain.
It is accordingly a general object of the present invention to overcome the problems caused due to free movement of shorter pins of the conventional rocker joint silent chain.
A more specific object of the present invention is to provide a rocker joint silent chain which is capable of preventing generation of high-frequency noise resulting from free movement of a shorter pin of each rocker joint, without increasing the number of parts of the silent chains thereby lowering the overall transmission noise level of the chain greatly, enabling smooth articulate movement of the interleaved link plates, and providing a prolonged service life of the chain.
To achieve the foregoing objects, according to the present invention, there is provided a rocker joint silent chain comprising: a plurality of sets of link plates interleaved with other sets of link plates, each link plate having a pair of spaced engagement teeth and a pair of spaced pin-accommodation holes; a plurality of pairs of guide plates located outside the sets of link plates in the widthwise direction of the silent chain, each guide plate having a pair of spaced pin-accommodation holes; and a plurality of rocker joints inserted in the pin-accommodation holes of the link plates and the pin-accommodation holes of the guide plates to connect the interleaved sets of link plates and the guide plates in an endless fashion. Each of the rocker joints is composed of a longer pin and a shorter pin which is smaller in length than the longer pin. The longer pin has opposite ends firmly fitted in a pair of aligned pin-accommodation holes of each pair of guide plates. The shorter pin has opposite ends projecting from opposite outer surfaces of each set of interleaved link plates and being in slight contact with inner surfaces of the pair of guide plates.
In one preferred form of the present invention, each end of the shorter pin has a flat end face, and the inner surface of each of the guide plates comprises a flat inner surface. The flat end face of the shorter pin and the flat inner surface of each guide plate are in surface contract with each other.
In another preferred form of the present invention, each end of the shorter pin has a flat end face, and each of the guide plates has a tongue-like stopper bent toward the flat end face of the shorter pin. The tongue-like stopper is in point contact with the flat end face of the shorter pin. The tongue-like stopper is integral with the guide plate and formed by cutting a portion of the guide plate adjacent each of the pair of pin-accommodating holes of the guide plate.
The term xe2x80x9cis in slight contact withxe2x80x9d used herein means that the opposite end surfaces of the shorter pin and the inner surfaces of the guide plate are not in pressure contact with each other but in light contact with each other to such an extent that the contact resistance between the end faces of the shorter pin and the inner surface of the guide plate can be neglected.
Since the opposite ends of the longer pin are firmly fitted in the pin-accommodation holes of the guide plates and thus secured to the guide plates, the width of the silent chain can be maintained uniformly, and a set of link plats which is offset half a pitch from the longer pin is permitted to pivot as the shorter pin rolls used in combination with the longer pin rolls on the longer pin.
Since the opposite ends of the shorter pin project from opposite outer surfaces of the set of interleaved link plates and are in slight contact with the inner surfaces of the guide plates located outside the link plate set, even when the silent chain is traveling in an advancing direction while vibrating in vertical and horizontal directions due to flattering or resonant vibration occurring at low operating speed range of the sprockets under the conditions that the chain tension is extremely small at the slack side of the silent chain and the chain is likely to become slack, free movement of the shorter pin inside the pin-accommodation holes of the interleaved link plates is completely prevented. This assists smooth pivotal movement of the interleaved link plates.